Tire Comprising A Textured Tread

ABSTRACT

Tire ( 1 ) comprising a tread ( 8 ), the tire comprising at least one groove ( 2 ), at least one wear indicator ( 3 ) disposed in the groove ( 2 ), the wear indicator comprising a contact face ( 7 ) intended to come into contact with a roadway when the tire reaches a wear limit, the groove ( 2 ) comprising a texture ( 4 ) produced integrally with a bottom ( 10 ) of this groove ( 2 ), said texture ( 4 ) surrounding the wear indicator ( 3 ) and contrasting with the contact face ( 7 ) of the wear indicator.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a tire, the crown of which has a treadprovided with grooves with textured zones.

PRIOR ART

In order to maintain the level of safety of a vehicle, it is appropriateto check the wear level of the tires regularly, and preferably beforeeach long journey. To this end, the motorist studies the surface of thetread of the tires and measures the height of the tread patterns. Thismeasurement is made easier by an element that is present on all types oftire: the weTRar indicator. The wear indicator makes it possible toevaluate the state of wear of the tires on the basis of a reliablereference. This indicator is typically disposed in the grooves of thetires. Thus, when the patterns of the tread are situated at the sameheight as the wear indicators (i.e., for example, in Europe, at a heightof at least 1.6 millimetres with respect to the bottom of the furrow),it is necessary to replace the tire(s).

The wear indicator is fitted at the bottom of furrows and is generallyin the form of a rectangle. It should be visible not only to the userbut also to third parties, for example in order to make it possible tocheck that the wear indicators comply with legislation. Therefore, it isimportant to have effective and reliable visual markers to make itpossible to locate the wear indicators quickly and easily. In somecases, the wear indicators of certain tires for passenger vehicles, inparticular models with a low-floor chassis, are less visible sincebodywork elements cover the top part of the tires. In this situation,the wear indicator becomes less visible. The user can then identify theposition of the wear indicator by referring to a marker situated in theshoulder zone. Such a marker can be formed by the well-known symbol“TWI” (for “Tire Wear Indicator), or any other symbol that is easilyrecognizable to users.

In other cases, the grooves of the tread are entirely covered withlight-absorbing textures, making it difficult, even sometimes extremelyso, to locate the wear indicator.

For example, the U.S. patent application Ser. No. 6,866,076 describes atire provided to reduce the resistance to a fluid flowing in thefurrows. To this end, the tire has textures at the furrow bottoms. Thefurrows of the tire are covered with small grooves or small ribs thathave a fixed depth in a range from 0.01 to 0.5 millimetres. Therefore,the resistance to the water flowing in the furrow is reduced. By virtueof this type of arrangement, it is possible to improve the performanceof the tire, for example in a wet environment. However, with such anarrangement, the wear indicator, which is disposed among the grooves, isnot very visible. Furthermore, the presence of the grooves close to thewear indicators can make the operations of checking the height of thewear indicators tricky. This is because the grooves constitute obstaclesthat can hamper good positioning of a measuring tool such as a ruler, amicrometer, or a calliper, and this can lead to inaccurate measurements.

The invention provides various technical means for remedying thesevarious drawbacks.

SUMMARY OF THE INVENTION

First of all, a first object of the invention consists in providing atire designed to make it possible to identify or locate tread wearindicators.

A further object of the invention consists in making it easier to verifythe compliance of the wear indicators with legal requirements.

Finally, another object of the invention consists in making it possibleto measure the height of the wear indicators positioned in a texturedsector.

To this end, the invention provides a tire comprising a tread, the tirecomprising at least one groove, at least one wear indicator disposed inthe groove, the wear indicator comprising a contact face intended tocome into contact with a roadway when the tire reaches a wear limit, thegroove comprising a texture produced integrally with a bottom of thisgroove, said texture surrounding the wear indicator and contrasting withthe contact face of the wear indicator.

Therefore, the textured surfaces of the grooves absorb light. Bycontrast, the smoother surfaces of the wear indicators allow betterreflection of the light. This creates a de facto contrast between thetwo surfaces and makes the wear indicator(s) more visible. The user canthus identify or locate the wear indicators of his tires more easily,making it less tedious to check tire wear.

Advantageously, the texture has a lightness known as first lightness(L*1) and the contact face of the wear indicator has a lightness knownas second lightness (L*2), the difference in lightness between the firstand second lightness being at least 5 units of lightness (on a scaleranging from 0 to 100). Such a difference in lightness makes it possibleto create a contrast effect that is easy for a user to find. Thiscontrast effect can advantageously serve to locate a specific point suchas a wear indicator, which is conventionally difficult to find on atread without a contrast effect.

The first lightness (L*1) is advantageously between 5 and 18 units, andpreferably between 8 and 16 units. The values tend towards black so asto absorb incident light well.

The lightness of the contact face (or second lightness) is between 20and 35 units. The values tend towards white so as to reflect incidentlight well.

According to an advantageous embodiment, the wear indicator comprises atleast one lateral face connecting the contact face of the wear indicatorto said bottom, said lateral face not having said texture. The texturedlateral face helps to improve the visibility of the wear indicator inthe groove.

According to another advantageous embodiment, the groove has atexture-free zone disposed between a zone provided with a texture and alateral face of the wear indicator, said texture-free zone having alength of between 3 and 10 mm.

Such a zone advantageously serves as a measuring zone, making it easierto check the compliance of the height H of the wear indicator, forexample during a step of checking on leaving the mould. The non-texturedappearance of the measuring zone makes it possible to precisely andreliably check the height H of the wear indicator.

Alternatively, the texture is recessed with respect to the bottom of thegroove. Such a recessed disposition reduces the risk of the flow ofwater being disrupted and does not disrupt the measurement of the heightH of the wear indicator.

Definitions

A “tire” means all types of resilient tread, whether or not it issubjected to an internal pressure.

A “rubber material” means a diene elastomer, that is to say, in a knownway, an elastomer which is based, at least partially (i.e. is ahomopolymer or a copolymer), on diene monomers (monomers bearing twoconjugated or non-conjugated carbon-carbon double bonds).

The “tread” of a tire means a quantity of rubber material delimited bylateral surfaces and by two main surfaces, one of which, referred to asthe tread surface, is intended to come into contact with a road surfacewhen the tire is being driven on.

The “sidewall” of a tire means a lateral surface of the tire, saidsurface being disposed between the tread of the tire and a bead of thistire.

A “texture” means an organized arrangement of a plurality of elements,all or some of the elements in the arrangement being the repetition ofone and the same basic element, for example a strand or a lamella.

A “strand” means a filiform element, the height of which is at leastequal to twice the diameter of a disc having the same surface area asthe mean cross section of the strand.

“Lamellae” means elongate strands which have a length at least equal totwice their height.

[0025]“Lightness” or “luminance” means the parameter which characterizesa surface to reflect light to a greater or lesser extent. Lightness isexpressed using a scale that ranges from 0 to 100 according to theL*a*b* colour model established by the CIE (International Commission onIllumination) in 1976. The value 100 represents white or totalreflection; the value 0 represents black or total absorption. In thiscolour model, a* and b* are chromaticity coordinates. The L*a*b* colourmodel also defines a chromaticity diagram. In this diagram, a* and b*indicate the direction of the colours: +a* goes towards red, −a* towardsgreen, +b* towards yellow, and −b* towards blue. The centre of thediagram is achromatic. Saturation increases as the values a* and b* riseand thus with increasing distance from the centre of the diagram.

DESCRIPTION OF THE FIGURES

All the embodiment details are given in the description which follows,which is supplemented by FIGS. 1 to 11, which are given solely by way ofnon-limiting examples and in which:

FIG. 1 is a partial view of a tread of a tire according to theinvention;

FIG. 2 is a cross-sectional view of an example of a wear indicatoraccording to the invention;

FIG. 3 is a cross-sectional view of a variant embodiment of the wearindicator from FIG. 2;

FIGS. 4 and 5 are cross-sectional views of two examples of texture-freewear indicators that are surrounded by measuring zones that are likewisetexture-free, inserted within a textured groove;

FIG. 6 shows a part of the texture of the groove according to a firstexemplary embodiment in which the texture has protruding elements in theform of strands;

FIG. 7 shows a part of the texture of the groove according to a secondexemplary embodiment in which the texture has protruding elements in theform of lamellae;

FIG. 8 shows a part of the texture of the groove according to a thirdexemplary embodiment in which the texture has protruding elements in theform of parallelepipeds;

FIG. 9 shows a part of the texture of the groove according to a fourthexemplary embodiment in which the texture has protruding elements inwhich the shapes and the distances between protruding elements arevariable;

FIG. 10 shows a part of the texture of the groove according to a fifthexemplary embodiment in which the texture has recessed elements whichare conical in this example;

FIG. 11 shows an enlarged view of a cavity of a recessed element of thetexture from FIG. 10.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a schematic depiction of a portion of a tread 8 of a tire 1.The tread 8 provides a surface for contact with the ground that is madeup of tops 9 of tread patterns. The bottoms 10 of tread patterns of thetire 1 form grooves 2 or furrows. The grooves 2 act as housings forpositioning the wear indicators 3. The grooves 2 can also be arranged indifferent ways in order to comply with specific functions. In theexample illustrated, the grooves 2 are circumferential and provided withtextures 4 at the groove bottoms 10. Such a covering has numerousfunctional and visual advantages. However, it is likely to affect thevisibility of the wear indicators 3. Therefore, according to theinvention, and as illustrated, the wear indicators 3, in particular thecontact faces 7 of the wear indicators, are advantageously texture-freeand have a surface that produces a contrast in lightness with theadjacent surface of the textured furrows. The contrast effect betweenthe bottom of the furrows and the wear indicators 3 allows the latter tobe made clearly visible, making it easier to locate them. Such a featureis particularly advantageous when the tread 8 is in a context in whichvisibility is limited.

As illustrated in FIG. 2, the texture-free wear indicator 3 is arrangedin a groove 2 provided with a texture 4. The lack of texture on the wearindicator 3 makes it possible to create an accentuated contrast withrespect to the textured groove 2.

A wear indicator 3 may have textured surfaces, such as a lateral face 6,for example. FIG. 3 illustrates such an exemplary embodiment. However,it is preferable for the contact face 7 (or functional part) of the wearindicator to be texture-free such that the contrast with the texture 4of the groove is accentuated. The integration of texture-free wearindicators 3 into textured grooves 4 has the effect of accentuating thevisibility of the wear indicators 3 by contrast effects, notablylightness. The wear indicators 3 are thus more clearly visible.

The abovementioned contrast effect arises from the fact that thelightness of the zones provided with textures is less than that of thetexture-free zones. Various arrangements or configurations of textures 4make it possible to produce such an effect, as described below inrelation to FIGS. 6 to 11.

The appropriate appliance for measuring the lightness is aKonica-Minolta CM 700D spectrocolorimeter (registered trade mark). Thisappliance is suitable for measuring:

the lightness L*1, L*2 of the zones of the groove (zones covered withthe texture, zones not covered with the texture);

a component a* which defines a first colour shade between red and green;

a component b* which defines a second colour shade between yellow andblue.

Said appliance is positioned on the part of the tire to be measured andsaid appliance gives the values of the three parameters L*, a* and b*relative to the texture. These measurements are taken notably using the“SCI” (specular component included) mode, set at an angle of 10° andwith a D65 type light setting (setting as defined by the InternationalCommission on Illumination, CIE). By virtue of this appliance, thelightness of the textures of the groove 4 is measured, this then beingcompared with the lightness of the texture-free parts of the wearindicator.

The arrangement that promotes the visibility of the wear indicators 3 atthe bottom of the groove 4 described above can advantageously be usedfor any type of tire 1.

FIGS. 4 and 5 illustrate schematic cross-sectional depictions of anotherembodiment of the wear indicators 3 according to the invention.Texture-free zones 5 are left clear in the immediate vicinity of thewear indicator 3 in order to make it possible to very precisely measurethe height H of the latter reliably and repetitively during a step ofchecking the wear indicator during the process of manufacturing thetire. In the exemplary embodiment in FIG. 4, the base of the textures inthe bottom of the groove 10 is situated in the same radial position asthe measuring zone 5 adjoining the wear indicator 3. In the example inFIG. 5, the tops of the textures in the groove are situated in the sameradial position as the measuring zone 5 adjoining the wear indicator 3.In these two exemplary embodiments, the measuring zone is substantiallyflat and texture-free.

FIGS. 6 to 11 illustrate examples of textures 4 that can be disposed inthe groove 2 according to the invention.

FIG. 6 illustrates an embodiment in which the texture has a plurality ofstrands 11. The strands 11 are distributed through the texture at adensity at least equal to one strand per mm², each strand having a meancross section S of between 0.0005 mm² and 1 mm². It will be noted thatthe mean cross section of each strand corresponds to the mean of thecross sections S measured at regular intervals from the base of thestrand. The strands have a conical overall shape with a cross sectionthat decreases over the height Hb of these strands.

FIG. 7 illustrates an embodiment in which the texture has a plurality ofmutually parallel blades 12, the spacing of the blades 12 in the texturebeing at most equal to 0.5 mm, each blade 12 having a mean width ofbetween 0.02 mm and 0.5 mm. It will be noted that the mean widthcorresponds to the mean of the widths I measured at regular intervalsover the height HI of the blade, the height of each blade being between0.05 and 0.5 mm.

In another variant embodiment, the texture has a combination of strands11 and/or blades 12.

The invention is not limited to the examples described and shown andvarious modifications can be made thereto without departing from itsscope. Thus, according to another non-limiting variant embodiment, theblades 12 from FIG. 7 can be discontinuous. They have a flat partbetween one another. They can also have cross-sectional differencesbetween one another. In addition, the blades can have curves or angles,notably along their length. They can also have a variable length.

In the example in FIG. 8, the textures have a parallelepipedal crosssection 13 having a side length C of between 0.05 mm and 0.5 mm and aheight Hp of between 0.05 mm and 0.5 mm, the distance Dp between twoadjacent cavities in the texture being between 0.05 mm and 0.5 mm.Alternatively, the cross section of the textures may be circular,polygonal (for example hexagonal). With the square or polygonalstructures, it is possible to more easily organize the elements withrespect to one another so as to limit the surface area of theintermediate zones between the elements.

In the variant in FIG. 9, the elements 14 have mutually variable shapesand distances. This variant makes it possible to render the details ofthe texture 4 less visible.

FIG. 10 illustrates a texture according to another non-limiting variantembodiment. In this variant, the texture is formed by a plurality ofcavities 16. The cavities 16 are in this case in the form of cones whichextend into the depth of the surface and open onto this surface, formingcircular openings 15. The cavities 16 thus have a cross section whichdecreases with depth. It will be noted that, in this variant, theopenings 15 of the cavities 16 are not in contact. The openings 15 areseparated by intermediate zones 17. Moreover, the openings 15 aredistributed regularly such that the distance d between each opening 15is similar overall.

FIG. 11 is an enlarged view of the texture in FIG. 10. In this case, allor some of the cavities have at least one wall 18 which, in crosssection, forms an angle β of between 10° and 60° with respect to adirection Z perpendicular to the texture.

The figures and their descriptions given above illustrate the inventionrather than limit it.

The reference signs in the claims are entirely non-limiting. The verbs“comprise” and “have” do not exclude the presence of elements other thanthose listed in the claims.

REFERENCE NUMERALS EMPLOYED IN THE FIGURES

1 Tire

2 Groove

3 Wear indicator

4 Texture

5 Texture-free zone

6 Face of the wear indicator

7 Contact face of the wear indicator

8 Tread

9 Top of tread pattern

10 Bottom of groove

11 Strands

12 Blades

13 Parallelepipedal cross section

14 Protruding elements

15 Openings

16 Cavities

17 Intermediate zones

18 Cavity wall

1. A tire comprising a tread, the tire comprising at least one groove,at least one wear indicator disposed in the groove, the wear indicatorcomprising a contact face adapted to come into contact with a roadwaywhen the tire reaches a wear limit, wherein the groove comprises atexture produced integrally with a button of said groove, said texturebeing organized arrangement of a plurality of elements, all or some ofthe elements of the arrangement being the repetition of a single baseelement, such as a strand or a lamella, said texture surrounding thewear indicator and contrasting with the contact face of the wearindicator.
 2. The tire according to claim 1, wherein the texture has alightness known as first lightness (L*1) and the contact face of thewear indicator has a lightness known as second lightness (L*2), whereinthe difference in lightness between the first and second lightness is atleast 5 units of lightness.
 3. The tire according to claim 2, whereinthe first lightness (L*1) is between 5 and 18 units.
 4. The tireaccording to claim 1, wherein the lightness of the contact face isbetween 20 and 35 units.
 5. The tire according to claim 1, wherein thewear indicator comprises at least one lateral face connecting thecontact face of the wear indicator to said bottom, said lateral face nothaving said texture.
 6. The tire according to claim 5, wherein thegroove has a texture-free zone disposed between a zone provided withsaid texture and said lateral face of the wear indicator, saidtexture-free zone having a length of between 3 and 10 mm.
 7. The tireaccording to claim 1, wherein the texture comprises a plurality ofstrands, said strands being distributed through the texture at a densityat least equal to one strand per mm², each of said strands having a meancross section S of between 0.0005 mm² and 1 mm².
 8. The tire accordingto claim 1, wherein the texture comprises a plurality of mutuallyparallel blades, the spacing of the blades in the texture being at mostequal to 0.5 mm, each said blade having a mean width of between 0.02 mmand 0.5 mm.
 9. The tire according to claim 1, wherein the textures havea parallelepipedal cross section with a side length C of between 0.05 mmand 0.5 mm and a height Hp of between 0.05 mm and 0.5 mm.
 10. The tireaccording to claim 1, wherein the texture is formed by a plurality ofcavities, said cavities being in the form of cones, said cavitiesextending into the depth of the surface and opening onto said surface,forming circular openings.
 11. The tire according to claim 2, whereinthe first lightness (L*1) is between 8 and 16 units.